The invention relates to a parison stick for an injection-blow moulding machine of a hollow body in plastic material, in particular a bottle of large size or having a double body, that is to say having two cavities connected via a bottle neck.
Hitherto, when produced by extrusion blow moulding, such bottles have defects of form, poor concentricity of the bottle neck and of the pouring neck, and variable wall thickness.
This results in considerable waste and a high manufacturing cost.
In order to remedy the inherent drawbacks of extrusion-blow moulding, some double-body bottles are produced by injection-blow moulding. When implementing such a process, it is necessary firstly to mould the first body, then to mould the second body and thereafter to assemble the two bodies. Injection-blow moulding thus requires two sets of equipment, which leads to a relatively high manufacturing cost.
Moreover, since the container is produced in three stages, this involves handling costs which increase the cost price.
In order to remedy this drawback, the invention aims to provide a parison stick which permits the injection-blow moulding of a double-body bottle in a single operation.
To this end, the invention relates to a parison stick for injection-blow moulding of a hollow article in plastic material, having a hollow cylindrical body comprising a portion for connection to an injection-blow moulding machine and extended axially by a portion for positioning in the wall of an associated mould of the machine, itself extended axially by a blow-moulding portion intended to be received in the cavity of the mould, and comprising first means for intermittent blow moulding, via a first blow-moulding opening, of a parison previously injected around the blow-moulding portion, these first means being arranged in the body of the parison stick, characterised in that the parison stick comprises, arranged in the body, second means for intermittent blow moulding, via a second blow-moulding opening, the first and second openings being distinct and spaced axially with respect to one another.
According to other features:
the blow-moulding means each comprise a channel connecting the associated opening to a common air-feed chamber and an obturator of the said opening connected to actuating means controlled by a control member of the machine;
the actuating means are controlled so as to simultaneously actuate the two obturators;
the air-feed chamber is located in the connection portion and is open on the radial free-end face of the latter in order to communicate, when positioned on the machine, with an air intake of the machine, the end of the chamber opposite the opening consisting of a wall pierced with an opening communicating with an axial bore passing through the body of the parison stick, and the actuating means are arranged in the chamber;
each obturator is of the type comprising a valve whose stem is connected to the actuating means and whose head interacts with a seat delimiting the associated opening, each valve being elastically returned against its seat in the closed rest position;
the actuating means comprise a thrust member mounted slidably in the chamber in order to be controlled by the control member of the machine, the thrust member having a radial thrust face located at that end of the latter which is distant from the opening, the stem of the valve of the first blow-moulding means consisting of a rod fixed to the thrust member and extending coaxially with the parison stick as far as the end of the latter delimiting the first opening, and comprise a guide member fixed in the chamber beyond the thrust member starting from the opening and pierced with an axial bore intended to have the rod pass through it and with longitudinal bores parallel to the axis of the parison stick, a bar being mounted slidably in each longitudinal bore and possessing an end bearing against the thrust face of the thrust member and an opposite end bearing against a radial end face of the valve stem of the second blow-moulding means;
the valve stem of the first blow-moulding means is arranged in a coaxial tube fixed on the guide member, the play between the valve stem and the inner wall of the tube forming the said channel of the first means, the tube having an end face delimiting the first opening located outside the body of the parison stick, and the valve of the second blow-moulding means consists of a sleeve mounted slidably between the tube and the inner wall of the body of the parison stick, the sleeve having an end located in the chamber between the base and the guide member in order to interact with the bars, and an opposite end which is widened in order to form a valve head intended to interact with the end face of the body of the parison stick which forms a valve seat, the channel of the second blow-moulding means being delimited between the outer wall of the sleeve and the inner wall of the body;
a ring is arranged at the end of the sleeve located in the chamber and comprises a collar, the valve of the second blow-moulding means being returned elastically by a helical spring arranged between the base of the chamber and the collar, the valve of the first blow-moulding means being returned elastically by a helical spring arranged between a shoulder of the guide member and the thrust member.
The invention also relates to an injection blow-moulding machine equipped with a mould intended to produce a bottle having a volume and a lower volume in mutual communication via a neck of small diameter, the blow moulding being carried out with the aid of a parison stick as described above and the moulding cavity of the mould comprising two volumes defining the shape of the bottle, the first blow-moulding opening of the parison stick being located in one of the volumes and the second opening in the other of the said volumes.